A conventional exercise device employing belt and wheels generally includes a wheel with radial blades extending outward form the wheel and a belt is connected between a pulley mounted to a hub of the wheel and another pulley mounted to a shaft. The diameter of the two pulleys are different so that when the user runs on the belt, the wheel is rotated. The radial blades cause air resistant force. However, the resistance force is fixed and cannot be adjusted. Therefore, the exercise device cannot meet different users' needs. Although another exercise device disclosed in Taiwanese utility model patent publish number 292569 partially resolves the shortcomings mentioned, it involves too many parts and employs torsion springs to control the resistance force. A frequent maintenance is required.
The present invention intends to provide a resistance adjusting device for an exercise device wherein the users simply pull a cable to control a distance between a metal board and magnetic members on the wheel, the resistance is controlled.